Welcome,
Get your gait analysed so at least you know what ype of shoe you need - if you are a bit strapped for cash you can always take the shops advice but buy on the net. Blisters aren't a reliable indication of overpronation.
Aim to add 5 - 10 minutes each week to your longest run - never increase by more than 10% each week. Have a look at some training plans
www.halhigdon.com and aim to do a race within the next 8 weeks or so to keep you motivated.
There a re lots of running shops in London: Sweatshop, Run & Become, London Marathon Store, Runners Need...there are probably more but start with these you can google them to get their addresses.
Enjoy your running.